Gulf of Maine Seasonal Sea Surface Temperature Update

Seasonal Patterns in Sea Surface Temperatures

Author

Adam Kemberling

Published

January 6, 2025

Fall 2024 Highlights

For this seasonal report we present an analysis of sea surface temperature (SST) for fall 2023-2024, defined as the period extending from (September 1, 2024 - November 30, 2024).

Winter is an important time of year for the Gulf of Maine. During this time of year, SSTs are typically falling, weakening the stratification of surface waters from deeper waters that occurs during warmer months. The breakdown of stratification allows for vertical mixing in the water column, which helps transport important nutrients up into the near-surface waters. These nutrients fuel the spring phytoplankton blooms that support the high productivity in the region. Vertical mixing may be enhanced in winter with the help of Nor’Easters, which are most common this time of year and stir up the water column with rough seas and strong winds.

This year, the average SST for the Gulf of Maine was 57.86°F. This seasonal average temperature was 1.33°F above the 1991–2020 climatological reference period (CRP) fall average of 56.53°F.

Weekly Temperatures

Table 1 highlights how the SST for each week this fall compares to the 1991-2020 CRP for the area shown in Figure 8. The observed SST, long-term average SST, and SST anomalies (i.e., departures from the long-term average SST) are shown.

fall average SST were on average 1.33°F below normal, with weekly SST anomalies ranging from -1.68°F to +0.41°F; all but one week at the end of 2023 recorded SSTs that were below the 1991-2020 average.

Table 1:
Average weekly sea surface temperatures in the Gulf of Maine
One-Week Period	Observed Temperature	Climatological Average	Temperature Anomaly
Table 1. Weekly Average Sea Surface Temperatures - Fall
(September 1, 2024 - November 30, 2024)
Sep 01 - Sep 07	64.00°F (17.80°C)	62.50°F (16.90°C)	1.55°F (0.86°C)
Sep 08 - Sep 14	63.50°F (17.50°C)	61.80°F (16.50°C)	1.76°F (0.98°C)
Sep 15 - Sep 21	63.50°F (17.50°C)	61.00°F (16.10°C)	2.47°F (1.37°C)
Sep 22 - Sep 28	60.50°F (15.90°C)	60.10°F (15.60°C)	0.44°F (0.24°C)
Sep 29 - Oct 05	61.70°F (16.50°C)	59.00°F (15.00°C)	2.65°F (1.47°C)
Oct 06 - Oct 12	61.00°F (16.10°C)	57.90°F (14.40°C)	3.11°F (1.73°C)
Oct 13 - Oct 19	58.00°F (14.40°C)	56.70°F (13.70°C)	1.29°F (0.71°C)
Oct 20 - Oct 26	56.60°F (13.70°C)	55.40°F (13.00°C)	1.17°F (0.65°C)
Oct 27 - Nov 02	55.60°F (13.10°C)	54.20°F (12.40°C)	1.37°F (0.76°C)
Nov 03 - Nov 09	54.70°F (12.60°C)	53.10°F (11.70°C)	1.56°F (0.87°C)
Nov 10 - Nov 16	52.40°F (11.30°C)	52.00°F (11.10°C)	0.38°F (0.21°C)
Nov 17 - Nov 23	50.70°F (10.40°C)	51.00°F (10.60°C)	-0.30°F (-0.16°C)
Nov 24 - Nov 30	49.90°F (9.96°C)	50.00°F (10.00°C)	-0.12°F (-0.07°C)
Data Source: NOAA OISSTv2 Daily Sea Surface Temperature Data.
Climatological Reference Period: 1991-2020.

Monthly Statistics

Table 2 shows monthly average SST for fall 2024. December SSTs were slightly below the 1991-2020 CRP, but the average SST anomalies for January and February were near or more than 1°F below the 1991-2020 CRP.

Table 2:
Average monthly sea surface temperatures in the Gulf of Maine
Month	Rank (1982-2024)	Observed Temperature	Climatological Average	Temperature Anomaly
Table 2. Monthly Average Sea Surface Temperatures - Fall
(September 1, 2024 - November 30, 2024)
September	10	62.80°F (17.10°C)	61.20°F (16.20°C)	1.57°F (0.87°C)
October	7	58.60°F (14.80°C)	56.70°F (13.70°C)	1.92°F (1.07°C)
November	16	52.20°F (11.20°C)	51.70°F (11.00°C)	0.48°F (0.27°C)
Data Source: NOAA OISSTv2 Daily Sea Surface Temperature Data.
Climatological Reference Period: 1991-2020.

How Does this Fall Compare to the Past?

2024 was the 10th warmest (18th coolest) fall season observed in the Gulf of Maine during the 41 years we have satellite data to analyze, a departure from fall seasons in recent years, which experienced well-above average SSTs.

Figure 1: A ranking of the 25 warmest winter seasons for the Gulf of Maine in the satellite record (1982-2023). 2023-24 was the twenty-third warmest winter on record.

Seasonal Trends and Long-Term Global Context

The Gulf of Maine is an area of particular interest to the scientific community because of the remarkable rate of warming it has experienced in recent years, coupled with its importance as a major driver for the regional economy.

Figure 2 illustrates the average fall temperature anomaly for each year in the Gulf of Maine since the beginning of the satellite record in 1982 overlaid with long-term SST anomaly trends for the Gulf of Maine (orange) and global oceans (blue) overlaid.

The fall rate of warming for the Gulf of Maine (1.08°F per decade) is roughly ~3.3x as fast as the warming rate for oceans globally (0.27°F per decade).

The fall SST anomaly for the Gulf of Maine in 2024 was 4.29°F cooler than that from 2022, the largest year-over-year decline in fall temperatures in the satellite record.

Figure 2: Average annual winter SSTs in the Gulf of Maine from 1982 through 2023-24 (black dots). The orange line indicates the trend for the full time series for the Gulf of Maine. The blue line indicates the trend for the full time series for the global oceans.

Marine Heatwave Conditions

The most commonly used definition of a “marine heatwave” (MHW) is when daily average SSTs exceeded the 90th percentile of a climatological (i.e., 30-year) average for at least 5 consecutive days. Gaps of 2 days or less in this threshold do not constitute a break in the MHW event. Using this broadly accepted definition, the Gulf of Maine has experienced MHW conditions for 10% of days this fall.

Figure 3: A timeseries of marine heatwave (MHW) conditions in the Gulf of Maine extending from December 1, 2023 through February 28, 2024. Black lines represent the long-term (i.e., 1991 – 2020) average SST, the 10th percentile, and 90th percentile for a given day in the Gulf of Maine; a solid line (red for marine heatwave or blue for a non-event) indicate the observed SST this year; red (above 90th percentile) and blue (below 90th percentile) shading illustrates how far the observed SST is from the climatological average.

Presenting SST conditions in terms of anomalies ( Figure 4 ) as opposed to absolute values ( Figure 3 ) illustrates in greater detail the magnitude of MHW conditions throughout the fall.

Figure 4: A timeseries of daily average SST anomalies in the Gulf of Maine (solid colored line) compared to the long-term climatological mean, 10th, and 90th percentiles (solid black lines) in the Gulf of Maine for the period December 1, 2023 through February 28, 2024.

Heatmap of Temperature Anomalies and Heatwave Events

Looking at the full record of daily SST anomalies in the Gulf of Maine (Figure 5), the distinct thermal regime shift beginning around 2010 is evident. Indeed, since 2012, the Gulf of Maine has experienced far more persistent MHW conditions (indicated by solid black lines) than at any other point in the satellite record.

Fall SSTs in the previous 3 years had been noteworthy for their extended MHW conditions, part of the long-term trend of unseasonably warm fall since 2012 (Figure 2). The relatively cold fall in the Gulf of Maine this year were an extension of cooler fall conditions, but stand out against above-average winter conditions since 2012.

Figure 5: Heat map of daily SST anomalies from the beginning of 1982 through March 2024. Not only do more large warm anomalies (darker reds) appear more frequently in recent years, but the frequency, duration, and intensity of marine heatwave events (black lines) in the Gulf of Maine has become more pronounced in the past decade.

Spatial Distribution of Seasonal Anomalies

From an aerial perspective, the Gulf of Maine experienced below-average SSTs during fall of 2024. In general, conditions were cooler in the deeper-water basins and warmer in shallow protected areas like the Bay of Fundy and Massachusetts Bay. The highest seasonally averaged SST anomaly in the Gulf of Maine was 2.29°F - located near the Bay of Fundy.

Figure 6: Map of average SST anomalies for each grid cell in the satellite record for spring 2023. The box outlined by the black dashed line denotes the region of study for the analysis (see Figure 8). Darker red regions indicate warmer anomalies. Black contours have been added at 100m and 200m depth

Monthly Temperature Anomalies

Average monthly SST anomalies are shown in Figure 7.

Figure 7: This series of maps shows the average monthly SST anomaly for December 2023, January 2024, and February 2024. The box outlined by the black dashed line denotes the region of study for the analysis. Darker red regions indicate warmer anomalies.

About the Updates:

Over the past decade, scientists have led a body of research that highlights the rapid pace of warming in the Gulf of Maine. To help keep you informed, we share seasonal and annual updates about conditions in the Gulf of Maine. For a full compilation of all of GMRI’s seasonal and annual Gulf of Maine warming updates, visit: https://gmri.org/warmingupdates/.

The Gulf of Maine Region

For analyses like these, it is important to be clear about the spatial extent that “defines” the Gulf of Maine (Figure 8), as different borders could produce different results. The spatial domain we use as the “Gulf of Maine” is outlined with the dashed line below. This area is consistent with previous seasonal and annual SST reports that scientists at GMRI have produced.

Data Sources:

NOAA High Resolution SST data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/data/gridded/data.noaa.oisst.v2.highres.html.

Citing This Work

If you would like to cite this report, please use:

Gulf of Maine Research Institute. 2024. Gulf of Maine Warming Update: Fall 2024

Note About the Data:

The figures in this report are created using remotely-sensed satellite data as part of publicly funded research efforts. Satellite SST data was obtained from NOAA’s National Center for Environmental Information (NCEI), with all maps and figures displaying NOAA’s Optimum Interpolation Sea Surface Temperature Data.

Note About the Data: The figures in this report are created using remotely-sensed satellite data as part of publicly funded research efforts. Satellite SST data was obtained from NOAA’s National Center for Environmental Information (NCEI), with all maps and figures displaying NOAA’s Optimum Interpolation Sea Surface Temperature Data.

A work by Adam A. Kemberling

Akemberling@gmri.org